Brake



v May 21, '1935- w. McoNKEY 2,001,971

BRAKE Filed April 2v, 1952 2 sheets-sheet 1` 6 I l 5 i v M@ 1224 v T'Z gufi? T'Zg 4 INVENToR. Ma/vrsa/vsnr M Mf'aA/KEY ATTORNEY Patented May 21., 1935 BRAKE Montgomery W. McConkey, South Bend, Ind., as-

signor to Bendix Aviation Corporation, South Bend, Ind., a corporation of Delaware Application April 27, 1932, Serial No. 607,879

4 Claims.

This invention relates to braking systems'and is illustrated as applied to a hydraulic braking system.

Devices have been proposed heretofore for use in combination with braking systems, for providing a relatively low mechanical advantage between the pedal and brakes during the initial brakingv stages and for providing a relatively7 high mechanical advantage during later braking stages. Usually these devices have been interposed in the connections between the pedal and the brakes and have been positioned adjacent to the pedal. Because of this construction, the high forces obtained must be transmitted through substantially the entire connecting mechanism with the consequent increased danger of breakage in the case of mechanical connections and of breakage and loss of uid in the case of fluid systems.

One of the objects of this invention is to provide novel means for obtaining relatively great mechanical advantage ratios for the application of the brakes.

A further object of this invention is to provide a two phase brake force transmission system adapted to be positioned within the wheel to be braked so as to minimize the friction developed by the high pressures attained and to minimize the danger of breakage of parts of the connections by reason of the high pressures developed.

A feature of the invention is a novel two phase wheel cylinder.

Further objects and features of the invention will be apparent after a reading of the subjoined specication and claims and after a consideration of the attached drawings in which:

Figure 1 is a plan view of the chassis of an automobile equipped with a hydraulic braking system illustrating my invention;

Figure 2 is ay View in vertical section and on an enlarged scale showing one of the wheels of the automobile of Figure 1;

Figure 3 is a view in vertical section and on a. still greater enlarged scale showing a fragment of the wheel cylinder of Figures 1 and 2;

Figure 4 is a view similar to Figure 3 showing a modified form of wheel cylinder, and

Figure 5 is a view of cylinder 24 with parts broken away and parts in section for showing the interior of the cylinder.

Referring in detail to the drawings; there is shown in Fig. 1, an automobile having a chassis (Cl. 18S-152) The wheels I8 and 20 are provided with brake drums 22 and positioned in each of the brake drums are shoes adapted to be operated by wheel cylinders 24 to which liquid is suppliedi through conduits 25 and 26 from a master cylinder 28, the latter being yoperated by a pedal 29.

As is shown more clearly in Figure 2, each of the drums 22 is provided with a pair of braking shoes 3|) and 3| secured to each other by an adjustable link 32 and normally held in the selected brakeolf position by springs 36 and 38. Theends of the shoes 30 and 3| opposite to the adjustable connection 32 normally bear against an anchor pin 42, and one of said ends or the other (dependent upon the direction of rotation of the drum during the braking operation) anchors against said pin in braking. 'I'he drum is provided with a backing plate 44 to which is secured the wheel cylinder 24. The cylinder 24 is provided with a pair of pistons to which there are connected respectively the piston rods 48 and 50, the latterbeing secured to the shoes 30 and 3| respectively.

Each'wheel cylinder 24 has at each end a piston such as the piston 52 (Fig. 3) which is formed with a central opening or passage 54 and which is provided with an annular packing cup 56. The ends of the cylinder 24 are formed with threaded openings such as 51 and into each of these openings there is threaded a sleeve 58 formed with ports 60. The piston rod comprises a tube 62 having its inner end threaded into the opening 54 and having its outer end enlarged to form a. pressure relief chamber or reservoir 64. The interior of the small portion of the tube 62 forms a passageway for fluid and this passageway is provided with a partition 66 and on opposite sides of the partition, the tube is formed with ports such as the ports 68 and the ports 'I0 respectively. At the point where the tube 62 merges into the chamber 64, a plug 12 is threaded into the tube 62 and normally resting upon this plug is aV piston comprising a rubber cup I8 and a guide 80. This piston is normally held against the plug 12 by a spring- 82 which bears at its opposite end against a vented fitting 84 screwed into the chamber 64 and having its opposite end secured to the shoe 3|.

In the operation of a brake system constructed as described above, movement of the pedal 29 forces liquid from the master cylinder 28 through the conduits 25 and 26 to each of the cylinders 24 and the liquid entering the cylinder through ports 86 forces the pistons 52 outward. Liquid trapped in the compartment between the piston 52 and the outer end of the cylinder passes through the ports 68 into the tube 62 and thence to the compartment at the center of the cylinder. However', inasmuchas the annular area at the end of the cylinders is smaller than the cross sectional area at the center of the cylinder, the pressure of the liquid causes the piston 52 to move outward. The effective area of the piston on which the pressure is acting is therefore an area corresponding to the cross section of the tube 6,2. The movementof the piston 52 outward forces the shoes intol contact with the drum. At about the same time that the shoes contact with the drum, the tube 62 moves so that the ports 68 are covered by the sleeve 58 and so that the ports'l register with the ports 60. Thereupon, further bypassing of liquid from the end of the cylinder to the center of, the cylinder is prevented but the liquid which is trapped in the end of the cylinder is allowed to pass through the tube 52, and through the ports |4 and 16 into the pressiu'e relief chamber 64. Thereafter, the liquid forced into the cylinder 24 acts effectively upon the whole surface of the piston 52, thereby moving the shoes at a slower rate but at increased pressure. Thereby the mechanical advantage through which' the pedal acts upon the brakes is in- `creased. The liquid forced into the relief chamber 64 forces the piston '|8-80 outward, this movement being allowed by the compression of the spring 82 and by the escape of air through the vented plug 84.

In Figure 4 a cylinder |24 is provided at each end with a piston |52 and a tube |62. The latter is formed with a pressure relief chamber |64 having its outer end closed by a Vented fitting |84. The fitting |84 is attached to the shoe |3| and together with the chamber |64 and the tube |62 serves as a piston rod. The tube |62 is formed with slots |88 and |90 and carries a valve plug |92. The latter is formed with bores |94, |96, |98, and 200 and is provided at itsouter end with a conical valve element 202 which normally contacts with a rubber cup |18 associated with a guide acted upon by a spring |92. The spring |82 is of pre-determined strength so that the valve member |92 is moved only when the pressure in the cylinder |24 reaches a certain predetermined value.

The bore |94 normally communicates with the center of the cylinder |24 and is arranged to intersect the'bore |96, the latter also intersecting the bore |98. The bore |98 normally registers with the slot |88 and thus normally liquid may pass from the center of the cylinder |46 to the end thereof. The bore 200 communicates with an annular space 204 formed adjacent the outer end of the valve member |92 but is normally cut off from communication with the cylinder |46. However, when the valve member |92 is moved outward by pressure, the bore 200 registers with the slot so that liquid trapped in the end of the cylinder may escape through the slot |90, the bore 200, and the recess 204 and thus past the valve member 202 to the pressure relief chamber It is believed that the operation of this modied form of my invention will be apparent from n the above description. Operation of a foot pedal similar to 29 causes a master cylinder such as 28 to force liquid into the cylinders |46 through the ports |86. The pressure of the fluid acting upon the pistons |52 moves each of the pistons inward and the associated tube |62, pressure relief chamber |64, fitting |84 and shoe |3| all move with the piston. As soon as suflicient resistance to movement of the -shoes `is encountered, the pressure of liquid in the system increases until it is suflicient to move each of the valve members |92 outward to close communication between the center of the cylinder |46 and the outer end thereof. Thereupon communication is established between the outer end of the cylinder and the pressure relief chamber |64. Thereafter, the liquid acts upon the pistons |52 to force the shoesinto contact with the drums with a very greatly increased pressure. It is to be understood that the above described embodiments of my invention are for the purpose of illustration only and various changes may be made therein without departing from the spirit and scope of the invention.

I claim: v

1. In a fluid braking system a wheel cylinder, a pair of pistons positioned in said cylinder and dividing it into a central compartment and two end compartments, a tube secured to each of said pistons to extend through the associated end compartments and formed with passageways, a pressure relief chamber associatedwith the outer end of each said tube, a small piston in each said chamber, a spring acting on each said small piston and means dependent on the phase of brake application for controlling said passageways to connect said end compartments to said central compartment or to connect said end compartments to said pressure relief chambers.

2. In a fluid' braking system; a cylinder; a piston in said cylinder, a tube secured to said piston and connected at times with the interior of said cylinder, a relief chamber associated with the outer end of said tube, and means for at times preventing passage of fluid from said cylinder through said tube into said relief chamber.

3. 'In a fluid braking system, a cylinder, a piston therein dividing said cylinder into two compartments, a tube associated with said piston, d

a pressure relief chamber associated with said tube, and a valve controlled by fluid pressure for connecting one of said compartments through said tube alternatively with the other compartment or with the pressure relief chamber.

said tube alternatively with the other compart- 4 ment or with the pressure relief chamber.

MONTGOMERY W. MCCONKEY. 

